The home team had a great chance to even things up in the 30th minute when Eli Dasa's ball found an unmarked Eran Zahavi whose shot went wide of goal.
"There's going to be a new Grand Slam champion. That's all I know right now. There's no past Grand Slam champions left in the draw," Zverev said.
In the women's singles, fourth seed Osaka survived a ding-dong battle against Kostyuk to emerge victorious 6-3, 6-7 (4), 6-2 after two hours and 33 minutes.
She will take on 15th-seeded Maria Sakkari of Greece in the last 16, who stunned Williams at the Western & Southern Open last month.
The 26-year-old clocked 1:05:34 to win the Prague 21.1km, a half marathon race featuring only female runners with no male athletes or pacers.
Xie and her teammates have two training sessions every day, one hour at 5:50am and two hours at 4pm.
Medvedev will next face fellow American Frances Tiafoe, and Thiem will take on Canada's rising star Felix Auger-Aliassime.
Behind the top three, Norris took fourth ahead of an out of sorts Bottas, who looked off the pace all day and appeared to suffer with handling and overheating problems.
R&F regained the lead at 39 minutes while Saba tucked an unchallenged shot into net, and left back Ye Chugui slotted in R&F's third goal from Saba's assist four minutes later.
Elsewhere, Canadian rising star Denis Shapovalov stunned seventh seed David Goffin of Belgium 6-7 (0), 6-3, 6-4, 6-3 to make last eight, while Croatia's Borna Coric also advanced.
The Aguascalientes-based outfit confirmed the appointment in a brief statement on social media. Earlier, Cruz told local media that he was looking forward to his first coaching role since parting ways with Dorados de Sinaloa last year.